The present invention relates to electronic devices, and, more particularly, to temperature detection by integrated circuits.
Various manufacturing processes require temperature monitoring for process control, and automatic (electronic) process control demands electronic temperature measurement. Further, microcontrollers and microprocessors require temperature measurements be available in digital format. However, current electronic circuits which measure temperature often consist of integrated circuits teamed with discrete temperature sensitive items such as thermistors and are inherently analog circuits. For example, FIG. 1a shows a thermistor bridge temperature sensor, and FIG. 1b shows a base-emitter voltage drop difference temperature sensor. An additional analog-to-digital converter would be needed to provide a digital output.
Many applications would benefit from a temperature detector (thermometer) implemented as a simple integrated circuit which requires no external components and which allows the temperature to be directly read digitally from the circuit. Further, such a self-contained temperature detector would permit integration into other integrated circuits as a sort of standard cell.
The present invention provides an integrated circuit temperature detector which runs an oscillator with a large temperature dependency up to a fixed count to thereby generate a time interval indicating temperature. The time interval may be used to gate an oscillator with a small temperature dependence to generate an output count (number of oscillations) varying with temperature (e.g.,approximately linearly). This provides for simple calibration due to the linearity and yields a direct digital expression of temperature. Alternative temperature detectors could use other temperature sensitive time interval generators such as an integrator of a temperature sensitive current. Digital temperature measurement permits use of the measurement as a direct input to a microcontroller or, more simply, as an address for a ROM to read out desired process control parameters.